The present invention relates to alternating current rectifying circuits and more particularly to improved techniques for providing current and temperature compensated rectifying circuits at low voltages.
Alternating current to direct current conversion circuits are generally well known and usually employ standard solid state diodes to perform the conversion. Diodes, however, do not have a linear voltage-current relationship at low conduction voltages and therefore fail to provide a proportional rectified voltage, particularly at low input voltages. In addition, the voltage-current relationship of a diode does not remain constant with temperature and thereby causes changes in the conduction voltage and conduction impedance to further reduce the accuracy of voltage-current rectification.
Various circuits have been proposed to overcome the above noted deficiencies with each exhibiting different degrees of success. As is known, if it is desired that the rectified output voltage be proportional to the input voltage for both large and small values of input voltage, then it is necessary to apply a separate voltage bias to the rectifier so that rectification begins at zero input voltage. One such circuit designed to perform that function couples a fixed bias voltage to one terminal of the rectifier to compensate for the conduction voltage. While this particular arrangement provides improved rectification characteristics, the same is still subject to inaccuracies since the bias voltage is fixed and remains independent of temperature and current changes in the conduction voltage and impedance.
While still many other circuits have been relatively successful in providing improved rectifier characteristics, there is still a need for new and improved devices capable of operation at both high and low voltages and over wide ranges of frequency. Accordingly, the present invention has been developed to overcome the specific shortcomings of the above known and similar techniques and to provide a technique for more precisely and reliably rectifying an alternating input voltage.